This invention relates to a process and apparatus for injection molding of injection molded parts of plasticized material, in particular plasticized liquid crystal polymers, wherein the plasticized material is injected into the mold cavity of a closed injection mold having at least two spaced apart infeed gates each associated with a plastification and injection device. Any shrinkage that occurs during the cooling of the injection molded parts can be compensated by further injection of the material.
The plasticized material referred to herein includes conventional plasticized thermoplastic material, granulated mixtures of isocyanate and a polyol, unburned ceramic compounds with added organic lubricants, elastomers, reinforced plastic material having added glass fibers, carbon fibers, metal powder, etc., that are completely reacted into polyurethane.
In accordance with current procedures for injection molding of injection molded parts of plasticized material, such material is extruded via an infeed gate into the mold cavity of a closed injection mold, and the shrinkage of the molded part that occurs upon cooling is compensated by the additional injection of plasticized material. And, injection molded parts can be molded of different plastic materials through multi-component injection.
Depending on the geometry, dimensions and wall thickness of the injection molded part during extrusion of the plasticized material into the closed injection mold, considerable injection pressures are required to produce fault-free injection molded parts. Correspondingly high mold locking pressures are therefore necessary to prevent the injection mold from inadvertently opening.
Currently it has been the practice to essentially direct attention to controlling and regulating the flow of the injection process in order to produce fault free, dimensionally stable and dimensionally accurate injection molded parts. A targeted flow of plasticized material into the mold cavity for a preset orientation of, for example, neutral fibers to effect optimum mechanical strength or loadability of the injection molded parts has up until now not been made possible.
From other fields of engineering of, for example, forged parts, it is known how to effect optimum strength or loadability of workpieces by correspondingly presetting the fiber orientation.